1. Field of the Invention
The present invention relates to a device for detecting a quantity of remaining ink, and more particularly, to a remaining ink detecting device for use in an ink jet recording apparatus for forming an image by emitting an ink droplet in response to a predetermined signal input.
The present invention further relates to an ink jet head cartridge with such a remaining ink detecting device incorporated therein.
The present invention further relates to an ink jet recording apparatus with such a cartridge mounted thereon.
2. Related Background Art
Ink, which is used, for example, in an ink jet recording apparatus for forming a desired high density image by emitting ink as droplets, is generally stored in a predetermined ink reservoir means, such as an ink cartridge. Various types of devices for detecting the level of residual ink stored in this reservoir means have been proposed.
One of the most commonly employed remaining ink detecting devices is designed to determine whether or not the amount of residual ink is less than a predetermined value on the basis of resistance detected in accordance with the quantity of residual ink existing between two electrodes.
Generally, recording heads mounted on the ink jet recording apparatuses are manufactured in the same manner as that in which semiconductor devices have been manufactured. Such recording heads are composed of a substrate made of silicon or the like and a member which forms ink passageways when it is attached to the substrate. On the substrate are disposed emission energy generating elements, such as electrothermal energy conversion elements, and function elements for driving these conversion elements, such as transistors and diodes. Ink is subjected to heat generated by the electrothermal energy conversion elements in the ink passageway.
FIG. 1 shows an equivalent circuit with electrical characteristics equivalent to those of the circuit for driving the above-described recording head. This driving circuit is designed to drive a recording head having 32 head ink outlets and 32 ink passageways which respectively communicate with these outlets. Individual ink passageways have corresponding electrothermal energy conversion elements R1 to R32, and transistors T1 to T32 which serve as switching elements.
FIG. 2 shows an equivalent circuit of the above-described remaining ink detecting device which is employed in a case where the above-described driving circuit is disposed on the substrate. In FIG. 2, reference numerals 1 and 2 denote electrodes for detecting resistance in accordance with the quantity of remaining ink. A reference numeral 3 denotes an electrode representing the substrate which forms the ink passageways of the above-described recording head and on which the driving circuit shown in FIG. 1 is deposited. A predetermined voltage or current is applied between the electrodes 1 and 2.
More specifically, between the electrodes 1 and 2, the ink flows stably, whereas between the electrodes 2 and 3, ink is affected by the vibrations caused by the discharge of ink and readily becomes unstable. Resistance R.sub.1-2 and resistance R.sub.2-3 representing the quantity of remaining ink respectively exist between the electrodes 1 and 2 and between the electrodes 2 and 3.
In the above-described circuit configuration, since the electrode 3 is floating and has infinite resistance, no current I flows between the electrodes 2 and 3. In consequence, the resistance detected by this remaining ink detecting device is determined only by the resistance R.sub.1-2 existing between the electrodes 1 and 2, and stable and accurate detection of the quantity of remaining ink can thus be performed.
For the purpose of meeting the demands for a reduction in size and simplification of the structure of recording heads and those for reduction in failures which occur during their manufacture, recording heads of the type in which electrothermal energy conversion elements and function elements such as switching transistors are disposed on the same substrate and are matrix driven have been developed and used recently. FIG. 3 shows an example of a driving circuit for such a recording head. Whereas the circuit shown in FIG. 1 has 32 switching elements T.sub.1 to T.sub.32, the circuit shown in FIG. 3 employs only 12 switching elements T.sub.a1 to T.sub.a4 and T.sub.b1 to T.sub.b8 to drive 32 electrothermal energy conversion elements R.sub.1 to R.sub.32.
However, in the recording head which employs this matrix driving method, the individual components are disposed at a high density, and this increases the possibility of a parasitic current flowing between adjacent diode cells in diodes D.sub.1 to D.sub.32.
More specifically, in the matrix driving method, (m.times.n) segments of electrothermal energy conversion elements are driven by using m block control terminals and n segment control terminals. FIG. 4A is a cross-sectional view of diodes employed in such a matrix driving method.
These diodes are driven in the manner described below. Although FIG. 4A shows only two diodes (cells), 32 diodes are, for example, disposed in a matrix in an actual recording head, as stated above.
Here, driving of electrothermal energy conversion elements RH1 and RH2, which form two segments in the same group, will be described.
When the electrothermal energy conversion element RH1 is to be driven, a switch G1 is first turned on to select the group, and a switch S1 is then turned on to select the electrothermal energy conversion element RH1. Turning of these switches causes a diode cell SH1 to be positively biased, supplying current to and thereby generating heat in the electrothermal energy conversion element RH1. This thermal energy generated changes the state of the liquid, thus generating a bubble and resulting in the emission of liquid from the outlet.
Similarly, the electrothermal energy conversion element RH2 is driven by selectively turning on switches G1 and S2 and thereby driving a diode cell SH2.
Since the individual diode cells SH1 and SH2 connected to the electrothermal energy conversion elements RH1 and RH2 are formed on the same substrate, the substrate is grounded, as shown in FIG. 4B, in order to electrically isolate the diodes.
In a case where the substrate is a N type Si substrate, the substrate is biased such that it has the highest potential, so as to electrically isolate the diodes.
However, in the case of a P type substrate which is grounded, the electrode 3 shown in FIG. 2, which represents the substrate, is not floating, but is grounded. In consequence, a resistance R.sub.2-3 affects the resistance detected by the circuit shown in FIG. 2, and the detected value is therefore not determined only by the resistance R.sub.1-2. As a result, the quantity of ink detected by measuring the resistance between the electrodes 1 and 2 is affected by the ink existing between the electrodes 2 and 3, and an accurate detection of the quantity of remaining ink is thus prevented.
Furthermore, bubbles may be generated as the gas dissolved in the ink changes with time, and such bubbles are easily attached to the above-described electrodes. These electrodes with bubbles attached thereto also prevent accurate detection of resistance.